The high incidence and prevalence rates, the years of morbidity, and the significant change in the quality of life make vertebral fractures in the elderly a major publiC health problem. The overall incidence rate of clinically diagnosed vertebral fractures is over l per 1000 person-years, and the incidence rate increases dramatically with age to approximately l fracture per 100 person-years in women over 80. The clinical consequences include a lower quality of life, loss of height, and acute and chronic pain. Vertebral fractures are attributed to age-related bone loss and changes in bone architecture, but little attention has been given to the etiology and biomechanics of these fractures. The first goal of this study is to derive a strong, significant predictor of vertebral fracture strength from dual--energy x-ray absorptiometry (DXA). New methodology will be used to determine the cross-sectional geometry of the vertebral body from lateral DXA scans. Fracture tests of cadaveric thoracic specimens will be used to develop the strongest predictor of ultimate load among DXA-based variables. The second goal will be to investigate the etiology of vertebral fracture in the elderly by surveying patients with vertebral fracture from the Beth Israel Hospital Emergency Unit and Wards. Control subjects with sudden onset of back pain will also be interviewed. Loads on the spine during the event will be estimated from the codified activities and anthropometric measures made during the survey. Quasi- static optimization models of spinal loading will be used. These loads on the spine will be compared between the two groups in an effort to identify those activities associated with increased risk of vertebral fracture. The third goal of this proposal is to test if both the ultimate vertebral load derived from DXA and the estimated applied load derived from mathematical models and surveys associate significantly with vertebral fracture in an elderly sample. The overall aim is to couple an investigation of an injury event with a measurement of vertebral strength. These concepts can be combined in one variable called the factor of risk, which is the applied spinal load divided by the estimated vertebral ultimate load. The significance and strength of the potential association between this factor of risk and the presence of vertebral fracture will be examined. The results of this investigation could have direct bearing on the prevention of injury in the elderly by identifying activities associated with an increased risk of fracture and also by identifying DXA-based properties of the lumbar spine that associate with fracture. If activities and individuals at increased risk are recognized, the results would offer support to the development and application of countermeasures that incorporate education to alter behavior or to therapeutic interventions to maintain bone mass and architecture.